1. Field of the Technology of the Invention
The present invention relates to an improvement in an ink recording apparatus which utilizes an electroosmotic phenomenon of a fluid ink.
2. Description of the Prior Art
The present inventor has already proposed an ink recording apparatus wherein a porous substance body which has two-dimensional spread is installed on a supporting substrate having a plural number of first electrodes insulated from each other, corresponding to the recording density, and a second electrode permeable to the fluid ink is located on this porous substance body at the surface that is opposite to the surface contacting the first electrodes, and the fluid ink is fed and impregnated into the above-mentioned porous substance body, and also signal voltages are applied between the above-mentioned first and second electrodes, thereby the above-mentioned fluid ink makes an electroosmotic travelling through the above-mentioned porous substance body to form a recording fluid ink part which is controlled corresponding to the above-mentioned signal voltages on a tip part of the above-mentioned first electrode, and also proposed an ink recording apparatus wherein this recording head is employed, thereby a recording medium is brought in contact with the tip part thereof to directly transfer the fluid ink or the fluid ink is flied and deposited onto the recording medium by means of electroosmosis or by Coulomb force due to a high electric field.
Here, the "Electroosmosis" is a general designation of the interfacial electrokinetic phenomena that, when a liquid substance is brought in contact with a solid substance, electric double layers are formed at their boundary surface, and when an electric field having a component parallel to this boundary surface is applied, the liquid substance moves in relation to the solid substance. The "Fluid ink" is a general description of a fluid with which recording is made on a recording media such as a recording sheet, and the fluid may or may not have color. For instance, it may be a transparent magnetic ink. Of course, it includes ordinary inks for use in ink-recording which contains coloring substance such as a dye and/or a pigment.
Conventionally, the above-mentioned ink recording head is operated in such a manner that the electroosmotic polarity of the fluid ink on the surface of the dielectric substance forming the surface of the supporting substrate and the electroosmotic polarity of the porous substance body are selected at the same polarity, and that signal of the ON voltage for making ink recording has the polarity by which the fluid ink makes an electroosmotic travelling from the second electrode side to the first electrode side through the porous substance body, and that the signal of the OFF voltage is of reverse polarity to the ON voltage and makes an electroosmotic travelling in the reverse direction to prevent an ink recording.
Then, as a result of the above-mentioned construction, on the part where the ON voltage is applied, the fluid ink is pushed out to the tip part side of the first electrode by an electroosmotic pressure, while on the part where the OFF voltage is applied, the fluid ink remaining on the tip part of the first electrode is sucked up toward the second electrode side through the porous substance body. In addition, on the tip part side of the first electrode, the fluid ink remaining on the part where the OFF voltage is applied makes an electroosmotic travelling to the part where the ON voltage is applied through the surface of the supporting substrate. Accordingly, on the tip part of the first electrode whereto the ON voltage is applied, an ink-converging action due to the adjacent OFF voltage and an ink-feed pumping action through the porous substance body are exerted, while on the tip part of the first electrode whereto the OFF voltage is applied, a suck-up effect toward the adjacent first electrode side whereto the ON voltage is applied and toward the second electrode side through the porous substance body is exerted.
Therefore, on the tip part of the first electrode whereto the ON voltage is applied, a high density of recording fluid ink part to be transferred or fly-deposited corresponding to the amplitude of the voltage thereof is formed, while on the part whereto the OFF voltage is applied, the recording fluid ink part disappears, thus the recording fluid ink part which is controlled corresponding to the signal voltage is formed.
Thus, the conventional ink recording head has an advantage that by selecting the ON voltage and the OFF voltage at suitable values respectively, a simple ink recording apparatus of high performance unlike the one of the conventional system can be constituted.
However, a problem was found that where the switching frequency of the signal voltage is high, where the gap between the first electrodes is wide and the recording density is low, or where the electroosmotic property of the surface of the supporting substrate is poor in comparison with that of the porous substance body, it is difficult to completely extinguish the remaining ink part on the gap at the tip part of the first electrode whereto the OFF voltage is applied, and because of transfer or fly-deposition of such fluid ink onto the recording medium, the resolution is remarkably reduced, resulting in a deterioration of an ink-recorded picture.